A fuel cell has been proposed as a clean, efficient, and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. An MEA and DM preassembled together with a subgasket for the separation of reactant fluids is known as a unitized electrode assembly (UEA).
In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. The electrodes of the fuel cell are generally formed from a finely-divided catalyst. The catalyst may be any electrocatalyst that catalytically supports at least one of an oxidation of hydrogen or methanol, and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, the electrodes, the DM, and a subgasket, for example, in the form of the UEA, are disposed between a pair of fuel cell plates. The pair of fuel cell plates constitutes an anode plate and a cathode plate. Each of the fuel cell plates may have a plurality of channels formed therein for distribution of the reactants and coolant to the fuel cell. The fuel cell plate is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In the case of a bipolar fuel cell plate, the fuel cell plate is typically formed from a pair of unipolar plates, which are then joined to form the bipolar fuel cell plate.
The fuel cell stack is generally connected to peripheral equipment for transfer of electrical power to electrical motors and circuitry, and for monitoring the performance of the fuel cell stack. Typical peripheral equipment includes cell voltage monitoring (CVM) equipment. Dimensional variations in the various fuel cell components, as well as dimensional variations in the peripheral equipment, can lead to interference. The interference results in difficulties in making proper electrical connections between the fuel cell stack and the peripheral equipment.
Known multicell CVM connector-to-plate interface concepts have used oversized contact pads or outward facing contacts in single rows, which are individually connected to each bipolar fuel cell plate. Such board-on-edge concepts place undesirable constraints on the stack repeat distance, and thus, the number of bipolar fuel cell plates that can be serviced by each electrical connection board.
There is a continuing need for a bipolar fuel cell plate that permits mating of the bipolar fuel cell plate and peripheral equipment despite dimensional variations.